Voltage regulating circuit for x-ray tubes



1955 w. H. BOLDINGH 3, ,7

VOLTAGE REGULATING CIRCUIT FOR X-RAY TUBES Original Filed March 3, 1959 I l'l'l'A'l'A'll 39 6 a 43 1111A All) 49 41 54 i so 54 g 9 I' II."""UIV/""" INVENTOR. WILLEM HOADIUS BOLDINGH AGENT United States Patent 3,164,723 VOLTAGE REGULATZNG CH'ZCUH FUR X-RAY TUBES Willem Hondius Boldingh, Emmhsingel, Eindhoven,

Netheriands, assignor to North American Philips Company, Inc., New Yorir, N.Y., a corporation of Delaware Original appiication Mar. 3, 1959, Ser. No. 795325, now Patent No. 3,027,460, dated M 27, 1962. Divided and this application Nov. 9, 196K, Ser. No. 163,982 Ciairns priority, application Netherlands Mar. 11, 195% 9 Ciairns. (6i. flit-4%) This invention relates to electrical circuit arrangements for supplying operating voltages for X-ray tubes of the type disclosed in my copending application Serial No. 796,925, filed March 3, 1959, now US. Patent 3,027,460, of which the present application is a division.

As stated in my aforementioned application, X-ray tube circuit arrangements usually comprise means for regulating the voltage between the anode and the cathode of the X-ray tube, i.e. the tube voltage. However, some X-ray devices are known in which the effective tube voltage always retains the same mean value, but these are usually small-size devices for special uses, such as dentistry, in which the objects or specimens contemplated to be examined are substantially of the same ilk. The

use of voltage-regulating means, permits, however, different medical examinations to be performed by means of one and the same X-ray device where different kinds of objects or specimens are to be examined.

Means for regulating the voltage is necessary in taking X-ray photographs if the required tube voltage diifers for each kind of object to be photographed. For example, the tube voltage required for fat patients is higher than that for thin patients. Furthermore, in choosing the voltage, allowance must be made for the different X-ray absorption characteristics of the various parts of the body.

When the desired tube voltage has been determined, it is customary to determine also the product of the tube current and the exposure time, and hence the load, in order to obtain a given blackening of the photographic plate. An X-ray device is usually provided with tables or graphs from which the adjustment of the load values may be derived for most examinations occurring in practics in which an X-ray photograph is to be taken.

Such a graph or table does not supply all the details which may aifect the absorption by rays of an object. Composing all the data for each individual object would become too expensive besides leading to results which are diificult to analyze and therefore diflicult to handle by the operator of the equipment. tions supplied by the graphs or tables are limited to the cases of most frequent occurrence. It is possible to distinguish a plurality of groups of objects for which the energy required for obtaining a given blackening of the photographic plate and the optimum tube voltage at which the photographs are taken differ considerably.

Examples of objects arranged in different groups or categories are the skull, the limbs, the thorax and the trunk. It is known that the blackening obtained with a given value of the tube voltage kilovolts (kv.) and load (mas) remains constant if it is ensured that the product kv. Xmas.

technique, for example, direct photograph or screen In View thereof, the indica ice image photography, and varies between 5 and 3. The influence of a variation in voltage upon the blackening is fairly considerable. In the case of direct photography, for which the higher values apply, it appears that a 1% voltage increase must be compensated by a 5% decrease in tube current in order to obtain the same blackening. As a result of the incompleteness of a graph or table which does not specify the optimum combination of tube voltage, tube current and exposure time for all possible cases which may occur, there is no certainty that the desired blackening is always obtained.

Making use of the influence of voltage variations upon the blackening, the disadvantage of false adjustment may be reduced by causing the tube voltage, during exposure, to vary from a minimum value to a maximum value which are, respectively, lower and higher than the optimum value derived from a table or determined in any other way.

The present invention relates to an X-ray circuit arrangement comprising means for regulating the voltage between the anode and the cathode of the X-ray tube, in which the tube voltage automatically increases during the exposure time for taking a photograph. A single control range in which the voltage can traverse all values which may be used for taking photographs aifords the advantage that the choosing of the voltage value may be omitted. However, in this case it is necessary for the highest and lowest voltages to be chosen for objects which differ most as to their kind and thickness. If then, the patient is exposed to X-rays which slightly contribute to obtaining the required blackening, such as in the case where a photograph is taken of a part of the body which is sufiiciently permeable only for rays produced at the higher voltage, or in the case where a short exposure time is necessary to avoid lack of definition due to movements of an object to be photographed the disadvantage is that the quantity of rays supplied to the patient is increased to an unnecessary extent. According to the invention, this disadvantage is substantially avoided by the use of means for regulating the tube voltage, which allows, inter alia, the tube voltage upon switching on the X-ray tube mining the correct photographingvoltage by the conven tional methods. The adjustments are not intended for individual cases but each combination of adjustments, owing to the rising voltage, is intended for a plurality of cases within the domains of application. For all cases classified in one group, the same variation of the tube voltage is used, a prescribed value being chosen for the milliamp-second product.

The above-mentioned and other features and objects of this invention will become apparent by reference to the following description taken in conjunction with the accompanying drawing, in which:

The single figure is a schematic diagram of the circuit arrangement of this invention comprising electrical voltage regulating means.

Referring to the figure, a high-vacuum regulating tube 38 has a control grid 39 which is. connected in the highvoltage lead in series with the X-ray tube 1. The grid voltage for the tube 38 is obtained by means of acircuit high voltagetransformer 2 is de-energized graphing process is' terminated.

tube 33, there is provided a variable resistor 46 which is 7 connected to an adjustable tapping point 56 on potentiometer 43. The supply circuit for a primary winding 48 of transformer 40, which is connected to the voltage mains, via the main switch 12, may be switched .on and off by means of a switch 49. The switch 49 is mechanically coupled to an operating switch-Stifor switching on the X-ray tube 1. The operating switch 50 operates electro-magnetically and includes an energizing coil 51, the energizing current of which may be supplied by means of a switch, illustrated, by way of example, as push-button switch 52. I i i Switching on the main switch 12- caus'es the'heating of thermionic cathode of X-ray tube 1 and the cathode 4510f regulating tube 38.' Subsequently, the time of exposure is determined by means'of a time selector 53. When push-button 52 is closed, the operating switchfii) closes the primary circuit of high-voltage transformer 2 and the X-ray tube 1 is switched on. When the operating a switch '50 is closed, push-button switch 52 is bridged by the contact 49 and the; circuit of the primary winding 480i transformer 4-4) is closed. After expiration of the.

exposure period determined by means of the time seleca a negative bias potential at the control grid 39. The connection 5d of resistor 46 may likewise be adjustable along the potentiometer 43, so that'the final value to which the voltage at the X-ray tube may increase may be regulated.

After the interrupting contact 55 of the time switch 53 has been'opened by the index 54-, which upon adjusting the exposure time is turned to the left and returns to its rest position during the time of photographing, so that the current supply to transformer 49 is interrupted, the capacitor 44 can'discharge through the potentiometer 43 and resistor 46,'so that after ashort time the arrangement is again ready for a new X-ra-y photograph.

To prevent the X-ray tube from being switched on again before thecapacitor 44 is discharged completely, it

is possible to provide a magnetic switch 57 by which capacitor 44 is bridged after the photograph has been taken. The short-circuit is removed at the beinning of a new photographing process 'by the winding 58, which when energized opens the switch 57, the winding 58 being connected in parallel with the potentiometer 43. 1 a As. disclosed in the previously mentioned U.S.-Patent 3,027,460, a variable resistor having a rotary contact may also be utilized asa time limiter, if use is made of the classificationofthe object groups according to the ex-' posure times usually employed in practice. In order to avoid lack'lof definitiondue'to movement of theobject to be photographed, the exposure time must be very short.

' In other cases, in which moving parts are not present, the

tor 53, an index 54 interrupts a contact 55 which is connected in series with the take-over contact 49' of pushbutton switch 52 and the energizing current for the coil 51 of operating switch 5% is interrupted. Thereafter, the

During the photographing process, the transformer iti causes capacitor M'to be charged. The voltage atthe grid 39 is initially'negative with respect to the cathode 45 of the regulating tube-38, but as the charge increases,

the potential of the control grid 33 increases 'and' the internal-resistance of the'regulating tube 33 decreases. Thus, asthe voltage loss in tube 33 decreases, the voltage between the anode 3 and the cathode 5, of the X-ray tube 1 increases. Since the value of tube current also determines the-time of exposure, itmay in certain cases be important toregulate the rate of change of the variation 'of tube voltage. ,This is effected by means of resister '46 which determines the charging characteristic of "capacitor '44. A decrease inresistancevalue of resistor ifi'speeds up the increasing voltage atthe capacitor 44," so that the. rate of the increase in Voltageat the X-ray' tube "'1 may ;be regulated by choosing, difierent. values for V the resistor 46.

V In order. to'X-rayrelatively ,thin objects and objects and the photonot exceed a predetermined value.

exposure time may be longer, it being necessary in certain cases to expose'for a long time since the required load is high and the'current traversing the X-ray tube; must 1 While I have described above the principles of my in vention in connection with specific'apparatus, it is to be clearly understood that. this description is made. only 7 by way of. example and not as a limitation to'the scope the accompanying claims. a

of my invention as set forth in theobjects thereof and in I claim:

1. A, voltage ,fregulating .circuitjarrangement for an 'X-raytube-having an anode and a cathode, said X-ray tube being adapted to operate. at a desired operating voltage dependent upon the characteristics of an object to be X-ray-photographed during the time of exposure required forthe X-ray photograph said desired operating voltage having a value in a range of voltages from a minimum" voltage magnitude to a maximum voltage magnitude,

secondary winding connected between the anodeand cathode of said X-ray tube, first switch means and means for applyingavoltage across said primary winding through saidffirst switch means, means for. automatically varying v the voitageacross said X-ray tube'from said minimum d having alow X-ray absorbing characteristicfthe' quantity;

h of rays required to produce an optimumlbla'ckening'ofa 7 Jphotographic plate requires 'a shorter'expos'ure period thanfor athicker object or one which exhibits 6ater.

-ra'y" absorbent characteristic. Iii-the 'lattercase, the" radiation obtained at the lower values of tube voltage": are relatively valueless since they produce little or no blackeningof the photographic plate. *ThisTadiationunmagnitudelto said maximum magnitude during said time of exposure, sa d voltage varying means comprising an electrondischarge device having an anode, a cathode and a control grid, means connecting said discharge device in:

of the said device in a manner whereby said-grid voltage voltage 'at ;which thephotograph is taken .to beregulated.

- By displacing the adjustable tapping point'of "comiection, 47 along thepotentiometer: 43,-itj is possiblej to adjust the.

"is initially negative with respect to said cathode at jthe' start of'said nine. of exposure and the voltage loss inthe j 7 said device. decreases. during the' s aid time of exposure thereby increasing the voltag'e across saidX-ray tube,'and' means for. varying said minimum and maximum magnh h i.

LA voltage regulating circuit arrangement for an X ray tub'e'having an anode and a cathode, said X ray tube 1 being adapted to operate aha de sired'operajtingvoltage dependent upon the characteristics of an object to be X rayfphotogtaphed during the time-oi exposure required for i the X-ray photograph, said desired operating voltage having a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X-ray tube, said voltage applying means comprising a high voltage transformer having a primary winding and a secondary winding connected between the anode and cathode of said X-ray tube, first switch means and means for applying an alternating voltage across said primary winding through said first switch means, and means for automatically varying the voltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising an electron discharge device having an anode, a cathode and a control grid, means connecting said discharge device in series circuit arrangement with said X-ray tube and said secondary winding, means for rectifying said alternating voltage to produce a rectified output voltage, a potentiometer having at least two tapping points, means for applying said rectified output voltage across said potentiometer, a variable resistor, a capacitor connected in series circuit arrangement with said variable resistor between two tapping points of said potentiometer and means for deriving from said variable resistor and a tapping point of said potentiometer a grid voltage for said discharge device with respect to the cathode of the said device in a manner whereby said grid voltage is initially negative with respect to said cathode at the start of said time of exposure and the voltage loss in the said device decreases during the said time of exposure thereby increasing the voltage across said X-ray tube, said minimum and maximum magnitudes being variable by adjustment of said two tapping points of said potentiometer.

3. A voltage regulating circuit arrangement for an X ray tube having an anode and a cathode, said X-ray tube being adapted to operate at a desired operating voltage dependent upon the characteristics of an object to be X-ray photographed during the time of exposure required for the X-ray photograph, said desired operating voltage having a value in a range of voltages from a minimum voltage magnitude to a maximum voltage magnitude, comprising means for applying a voltage across said X-ray tube, said voltage applying means comprising a high voltage transformer having a primary winding and a secondary winding connected between the anode and cathode of said X-ray tube, first switch means and means for applying an alternating voltage across said primary winding through said first switch means, and means for automatically varying the voltage across said X-ray tube from said minimum magnitude to said maximum magnitude during said time of exposure, said voltage varying means comprising an electron discharge device having an anode, a cathode and a control grid, means connecting said discharge device in Series circuit arrangement with said X-ray tube and said secondary winding, means for rectifying said alternating voltage to produce a rectified output voltage, a potentiometer having at least three tapping poin-ts at least two of which are adjustable, means for applying said rectified output voltage across said potentiometer, a variable resistor, a capacitor connected in series circuit arrangement with said variable resistor between two adjustable tapping points of said potentiometer and means for deriving from a common point in the series circuit arrangement between said capacitor and said variable resistor and a variable tapping point of said potentiometer a grid voltage for said discharge device with respect to the cathode of the said device in a manner whereby said grid voltage is initially negative with respect to said cathode at the start of said time of exposure and the voltage loss in the said device decreases during the said time of exposure thereby increasing the voltage across said X ray tube, said minimum and maximum magnitudes being variable by adjustment of said two variable tapping points of said potentiometer.

4. Apparatus for supplying an operating voltage to an X-ray tube having an anode and a cathode, the desired operating voltage of said X-ray tube being dependent upon the characteristics of an object to be X-rayed, said apparatus comprising input means for a source of electrical energy including means for applying an operating voltage to said anode of said X-ray tube, means for varying said operating voltage independently of the cathode heater current through a range of voltages between an end voltage of a predetermined minimum value and an end voltage of a predetermined maximum value during the time of exposure of said object to be X-rayed, electrical circuit means for adjusting one of said end voltage values, said circuit means being connected to said voltage varying means, and means for disconnecting said X-ray tube from said means for applying an operating voltage at the end of an exposure.

5. Apparatus for supplying an operating voltage to an X-ray tube having an anode and a cathode, the desired operating voltage of said X-ray tube being dependent upon the characteristics of an object to be X-rayed, said apparatus comprising input means for a source of electrical energy including means for applying an operating voltage to said X-ray tube, means for varying said operating voltage through a range of voltages between an end voltage of a predetermined minimum value and an end voltage of a predetermined maximum value during the time of exposure of said object to be X-rayed, electric circuit means for adjusting one of said end voltage values, said circuit means being connected to said voltage varying means and further comprising means for adjusting the rate of change of said varying operating voltage to a predetermined value correlated to the object to be X-rayed.

6. Apparatus for supplying an operating voltage to an X-ray tube having an anode and a cathode, the desired operating voltage of said X-ray tube being dependent upon the characteristics of an object to be Xrayed, said apparatus comprising input means for a source of electrical energy, means energized from said source for furnishing a varying operating voltage to said X-ray tube during the time of exposure of said object to be X-rayed, said varying operating voltage being variable through a range of voltage values between first and second end limit values, and means for independently adjusting said first and second end limit voltage values coupled to said means for furnishing a varying operating voltage, and means for disconnecting said X-ray tube from said last named means at the end of an exposure.

7. Apparatus for supplying an operating voltage to an X-ray tube having an anode and a cathode, the desired operating voltage of said X-ray tube being dependent upon the characteristics of an object to be X-rayed, said apparatus comprising input means for a source of electrical energy, means energized from said source for furnishing a varying operating voltage to said X-ray tube during the time of exposure of said object to beX-rayed, said varying operating voltage being variable through a range of voltage values between first and second end limit values, means for adjusting the rate of change of said varying operating voltage to a predetermined value correlated to the object to be X-rayed, and means for disconnecting said X-ray tube from said means for furnishing a varying operating voltage at the end of an exposure.

8. Apparatus for supplying an operating voltage to an X-ray tube having an anode and a cathode, the desired operating voltage of said X-ray tube being dependent upon the characteristics of an object to be X-rayed, said apparatus comprising input means for a source of electrical energy, means energized from said source for applying a voltage across said X-ray tube, means for continuously varying the voltage across said X-ray tube from a minimum voltage level to a maximum voltage level during the time of exposure of said object to be X-rayed, said voltage varying means comprising a variable impedance device serially connected in the anode-cathode circuit of said X-ray tube, the impedance of said variable impedance device being continuously variable from a maximum value to a minimum value during said time of exposure, 7

and means for adjusting said minimum and maximum voltage levels in accordance with the characteristics of a the object to be X-rayed.

9. Apparatus according to claim 8 further comprising means for adjusting the rate of change :of said continuously varying voltage, said latter means comprising a re- 

4. APPARATUS FOR SUPPLYING AN OPERATING VOLTAGE TO AN X-RAY TUBE HAVING AN ANODE AND A CATHODE, THE DESIRED OPERATING VOLTAGE OF SAID X-RAY TUBE BEING DEPENDENT UPON THE CHARACTERISTICS OF AN OBJECT TO BE X-RAYED, SAID APPARATUS COMPRISING INPUT MEANS FOR A SOURCE OF ELECTRICAL ENERGY INCLUDING MEANS FOR APPLYING AN OPERATING VOLTAGE TO SAID ANODE OF SAID X-RAY TUBE, MEANS FOR VARYING SAID OPERATING VOLTAGE INDEPENDENTLY OF THE CATHODE HEATER CURRENT THROUGH A RANGE OF VOLTAGES BETWEEN AN END VOLTAGE OF A PREDETERMINED MINIMUM VALUE AND AN END VOLTAGE OF A PREDETERMINED MAXIMUM VALUE DURING THE TIME OF EXPOSURE OF SAID OBJECT TO BE X-RAYED, ELECTRICAL CIRCUIT MEANS FOR ADJUSTING ONE OF SAID END VOLTAGE VALUES, SAID CIRCUIT MEANS BEING CONNECTED TO SAID VOLTAGE VARYING MEANS, AND MEANS FOR DISCONNECTING SAID X-RAY TUBE FROM SAID MEANS FOR APPLYING AN OPERATING VOLTAGE AT THE END OF AN EXPOSURE. 